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An athlete is working out in the weight room. He steadily holds 50 kilograms above his head for 10 seconds. Which statement is true about this situation? The athlete isn’t doing any work because he doesn’t move the weight. The athlete isn’t doing any work because he doesn’t hold the weight long enough. The athlete is doing work because he prevents the weight from falling downward. The athlete is doing work because 50 kilograms is a significant load to lift.


The athlete is sweating, straining, sweating, trembling and groaning. 
But if he passed high school physics, then he may remember that
'work' in physics means (force) x (distance).  If there's no distance,
then there's no work. 

He realizes that he isn’t doing any work because he's not moving the weight.


Related Questions

Posted in Physics

What happens when the temperature of an object increases? A. The particles move closer together. B. The particles move faster. C. The number of particles increases. D. The particles stop moving.

I believe the correct answer from the choices listed above is option B. When the temperature of an object increases, the particles move faster since kinetic energy of the molecules increases. Hope this answers the question. Have a nice day.

Posted in Physics

In 2004 astronomers reported the discovery of a large Jupiter-sized planet orbiting very close to the star HD 179949 (hence the term "hot Jupiter"). The orbit was just 19 the distance of Mercury from our sun, and it takes the planet only 3.09 days to make one orbit (assumed to be circular). What is the mass of the star? Express your answer (a)in kilograms and (b)as a multiple of our sun's mass.

  I'll tell you how to do it but you must crunch the numbers. 

Use Kepler's 3rd Law 

T^2 = k R^3 

where k = 4(pi)^2/ GM 
G =gravitational constant = 6.67300 × 10-11 m3 kg-1 s-2 
M = mass of this new planet 
pi = 3.14159265 
T =3.09 days = 266976 seconds 
R = (579,000,000km)/9 = 64333333.3 km 

a) 
Solve Kepler's 3rd Law for M. Your answer will be in kg 


b) 
mass of the sun = 1.98892 × 10^30 kilograms 
Form the ratio 
M(planet)/M(sun) 

Posted in Physics

A snowmobile has an initial velocity of 3.0 m/s Part 1: If it accelerates at the rate of 0.5 m/s/s for 7.0 sec, what is the final vel.? Part 2: If it accelerates at the rate of -0.60m/s/s, how long will it take to reach a complete stop?

Answer:

Part a)

v_f = 6.5 m/s

Part b)

t = 5 seconds

Explanation:

Part a)

As we know that

v_f = v_i + at

here we know that

v_i = 3 m/s

a = 0.5 m/s^2

t = 7.0 s

so we will have

v_f = 3 + (0.5)(7.0)

v_f = 6.5 m/s

Part b)

if finally the snowmobile comes to rest

So here we can say that

v_f = 0

v_i = 3.0 m/s

a = -0.60 m/s^2

so now we have

v_f = v_i + at

0 = 3.0 - (0.60)t

t = 5 s

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Posted in Physics

What are the characteristics of weight

Shape or texture...im just try....

Posted in Physics

Will upvote!! True or False- The parts of a mixture keep their own properties when they are combined.

I believe the correct answer is false. The parts of a mixture do not keep their own properties when they are combined. When they are combined, they exhibit or behave with different properties since each atom is bonded which gives them unique properties. Hope this helps.

Posted in Physics

. How much work in joules is done by a person who uses a force of 25 N to move a desk 3.0 m?

We Know, W = F * s
here, F = 25 N
s = 3 m

Substitute it into the expression,
W = 25 * 3
W = 75 Joule

So, your final answer is 75 J

Hope this helps!

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Explain Why must a cooling system do work to transfer thermal energy?

Although internal energy will not spontaneously flow from a cold region to a hot region, it can be forced to do so by doing work on the system.Refrigerators and heat pumps are examples of heat engines which cause energy to be transferred from a cold area to a hot area. Usually this is done with the aid of a phase change, i.e., a refrigerant liquid is forced to evaporate and extract energy from the cold area. Then it is compressed and forced to condense in the hot area, dumping its heat of vaporization into the hot area. ARE YOU FROM K12?

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A car starts from xi = 12m at ti = 0 and moves with the velocity graph shown in figure below. What is the objects position and t=3s and t=4s? Picture in comments below

Our starting velocity is V0 = 12m/s

There are 2 ways of solving this question
First is to use formula which connects starting speed, acceleration (which we would calculate from graph where we can see how speed changes) and time to calculate traveled distance.

S = V0 * t + 1/2*a*t^2

acceleration a is a = -4m/s^2

S(t=3s) = 18

On this value we add 12 initial meters of distance and we get S(t=3s) = 30 meters

For t=4s we get

S = 16 m

Plus initial distance of 12 m we get 30 meters

Answers are 30 and 28 meters.

------------------------------------------
second way is to find surface of graph bellow speed line for 3 and 4 seconds...

Posted in Physics

Please help! Find the tension in each cord in the figure if the weight of the suspended object is w = 210N A) Find the tension in the cord A for system (b). B) Find the tension in the cord B for system (b).

We have to solve the system of equations:
- T a * cos 60° + T b * sin 45° - 210 N = 0
- T a * sin 60° + Tb cos 45° =  0
------------------------------------------------------
- 1/2 T a + √2 / 2 T b = 210 N
- √3 / 2 T a + √ 2 / 2 T b = 0     / * ( - 1 )
---------------------------------------------------
- 1/2 T a + √2 / 2 T b = 210 N
√ 3 / 2 T a - √2 / 2 T b = 0
----------------------------------------
T a ( √3 / 2 - 1 / 2 ) = 210 N
0.366 T a = 210 N
T a = 210 N : 0.366
1 ) T a = 573.77 N
Ta * √3 / 2 = T b * √ 2 / 2
T b = ( 573.77 * 1.732 ) : 1.4142
2 ) T b = 702.7 N 

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Posted in Physics

If you increase the force on an item without changing the mass you increase acceleration? true or false?

(F)(M)=A
Force times Mass equals Acceleration.
The answer is TRUE. 
If the mass increases the number on the left side of the equation increases, thus increasing the right side as well.

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The acceleration due to gravity on Earth is 9.80 m/s2. An African elephant can have a mass up to 6,050 kg. What is its weight?

The weight on earth is equal to m*g, where m is the mass and g is the gravitational force. 6050 (m) * 9.8 (g) = 59290 Newtons.

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If two carts collide, what type of collision will conserve both momentum and kinetic energy? a. head on b. perfectly inelastic c. none d. perfectly elastic

The appropriate answer is d. perfectly elastic. When a perfectly elastic collision occurs both momentum and kinetic energy are preserved. Momentum is the mass of an object times its velocity while kinetic energy is the energy that a moving object has due to its motion. In an elastic collision kinetic energy would be converted to some other form of energy. 

Posted in Physics

What is meant by the following statement? "Acceleration is inversely proportional to mass."

Answer:

he gave the correct answer its just we had options when we were doing this assignment so thanks for going in depth

Explanation:

Ps Odsseyware

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Why doesn't an electromagnetic wave move as fast through a solid as it would a gas

Because in a solid the atoms are a lot closer together, and depending on the size, a lot more of them. In gas, there is in fact more atoms, but they are not as close together, making it easier of the waves to travel along.

Posted in Physics

A 10.00 g sample of a compound containing only carbon, hydrogen, and oxygen forms 23.98 g CO2 and 4.91 g H2O upon complete combustion. What is the empirical formula of the compound?

(23.98 g CO2) / (44.00964 g CO2/mol) × (1 mol C / 1 mol CO2) = 0.544881 mol C 
(0.544881 mol C) × (12.01078 g C/mol) = 6.54445 g C 

(4.91 g H2O) / (18.01532 g H2O/mol) × (2 mol H / 1 mol H2O) = 0.54509 mol H 
(0.54509 mol H) × (1.007947 g H/mol) = 0.54942 g H 

10 g total - 6.54445 g C - 0.54942 g H = 2.90613 g O 
(2.90613 g O) / (15.99943 g O/mol) = 0.18164 mol O 

Divide by the smallest number of moles: 
(0.544881 mol C) / 0.18164 mol = 2.9998 
(0.54509 mol H) / 0.18164 mol = 3.0009 
(0.18164 mol O) / 0.18164 mol = 1.0000 
Round to the nearest whole number to find the empirical formula: 
C3H3O 

Posted in Physics

Which scenario relates to Mayer and Salovey’s third component of emotional intelligence (regulating emotions)? A. gauging a friend’s anxiety in the absence of verbal cues B. reacting pleasantly to a friend’s practical joke C. understanding a friend’s problems and providing support D. determining the underlying cause of a friend’s nervous breakdown E. asking for a friend’s suggestion when working through a conflict

Option C i.e understanding a friend's problems and providing support is the correct answer.

Mayer and Salovey’s third component of emotional intelligence (regulating emotions) is the ability to Understand Emotions. So understanding a friend’s problems and providing support is the scenario relates to Mayer and Salovey’s third component of emotional intelligence (regulating emotions)

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A student hangs a mass of 150 g on a force table at an angle of 150 degrees . If she then hangs a mass of 220 g at 270 degrees. A) at what angle should she hang a mass of 195 g so that the ring is in equilibrium? B) Draw the vectors

Horizontally: 150g*cos150 + 220g*cos270 + 195g*cosΘ = 0 
cosΘ = 0.666
Θ = ± 48º 
Vertically: 
150g*sin150 + 220g*sin270 + 195g*sinΘ = 0 
sinΘ = 0.744 
Θ = 48º

Posted in Physics

A laser produces 20.0 mW of red light. In 1 hour, the laser emits 2.29 X 10^20 photons. What is the wavelength of the laser?

Using Planck's equation,

E = nhc / λ

Also, Power = Energy / time
E = 20 x 10⁻³ x 60 x 60
E = 108 J

108 = (2.29 x 10²⁰ x 6.63 x 10⁻³⁴ x 3 x 10⁸) / λ
λ = 4.22 x 10⁻⁷ m

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